There are a number of solid materials of commercial importance that are produced, shipped and stored in bulk in today's marketplaces that exhibit a dangerous potential for explosion. One such material is nitrogen-based fertilizers. For example, ammonium nitrate is an essential component for numerous nitrogen-based fertilizer products.
Ammonium nitrate based fertilizers have experienced widespread use and acceptance in the agricultural industry over the past several decades. However, despite its agricultural benefits, ammonium nitrate is a highly volatile and unstable material with explosive hazard characteristics. Indeed, despite its beneficial and critical role in agriculture, ammonium nitrate has become a vehicle for disseminating chaos and is widely recognized as one of the most significant threats to society, as demonstrated in a number of malicious attacks such as the Alfred P. Murrah Federal building in Oklahoma City, the Marriott Hotel in Jakarta, and the Sari Club in Bali. Ammonium nitrate mixed with fuel oil creates a powerful explosive, ANFO, which is a weapon of choice for acts of terrorism due to relatively low cost, availability, ease of assembly, and magnitude of destructive force released upon detonation.
In order to make ammonium nitrate fertilizers safe for consumer use, the explosive potential of the ammonium nitrate must be somehow controlled. Prior attempts to control the explosive potential of ammonium nitrate have included addition of desensitizing agents, such as polymeric coatings or diluents, or the substitution of alternative nitrogen sources. However, desensitizing agents are for the most part ineffective, costly, and may impart undesirable side effects. Even more, despite recommendations regarding reducing explosive potential of ammonium nitrate, attempts to control the sale of agricultural-grade product or to mandate addition of desensitizing agents have met with resistance stemming from a perceived negative impact on price and accessibility coupled with an apparent ineffectiveness of the proposed desensitizing agents when added at concentrations that are compatible with agriculture.
Alternate sources of nitrogen-containing fertilizers include potassium nitrate, urea and anhydrous ammonia. Alternatives such as anhydrous ammonia require increased infrastructure costs for distribution, are a concern due: to toxic fumes, suffer from potential volatile losses following application, and unlike ammonium nitrate, must be applied subsurface to croplands requiring more expensive application equipment with an accompanying increase in application costs. Other alternatives such as urea may be less effective due to ammonia volatilization, and indeed are also potentially explosive. For certain agricultural crops such as vegetables, tobacco, hay, and pasture lands, ammonium nitrate has distinct advantages in both economy and ease of application compared to potential nitrogen-fertilizer substitutes.
As another example, the dilution of ammonium nitrate with inert or thermally stable materials in order to reduce the potential for explosion is a common practice well known in the art. For example, ammonium nitrate marketed in Ireland, as well as most of Europe, is marketed at less than 79 weight percent of ammonium nitrate: that is, 78.5% ammonium nitrate and 21.5% thermally stable diluent. The diluent most commonly employed is calcium carbonate (lime). While the calcium carbonate does reduce the explosive potential, its added mining and crushing costs significantly increases the final delivery costs for an equivalent amount of ammonium nitrate. Even more, carbonates are easily evolved with acid to increase ammonium nitrate concentration. Thus, calcium carbonate is not an economically attractive diluent nor is it a totally effective blast mitigant. Still, it is used because alternative safe, effective, inexpensive, and agriculturally beneficial diluents are unknown to those skilled in the art.
As a further disadvantage, it should be appreciated that calcium carbonate may be easily removed: from the ammonium nitrate by adding an acid to the mixture. This converts the calcium carbonate (CaCO3) to calcium oxide (CaO) and carbon dioxide (CO2). The carbon dioxide is gaseous so the effective weight of the diluent is decreased and the concentration of the ammonium nitrate is effectively increased along with the explosive potential. In this way, it is possible to easily obtain a product having a higher weight percent of ammonium nitrate and thus higher explosive capabilities. Accordingly, the mixing of ammonium nitrate with calcium carbonate has little if any deterrent effect with respect to radical terrorist groups and others seeking to construct explosive devices.
Other attempts at controlling the explosive characteristics of ammonium nitrate have included the use of di- or mono-ammonium phosphate as a diluting material. It was originally thought that the addition of one or both of these chemicals at 5 to 10 weight percent would prevent ammonium nitrate from violently decomposing. However, it is now understood that the phosphate additives do not prevent the ammonium nitrate from exploding, and in fact, the energy release from an explosion of the ammonium nitrate/phosphate mix may be even greater than the energy release from pure ammonium nitrate. Furthermore, the ammonium phosphate additives can be easily removed from the ammonium nitrate/phosphate mix through the addition of calcium nitrate which in turn forms even more ammonium nitrate. Thus, it is clear that the phosphate additives do very little, if anything, to increase the stability of ammonium nitrate or deter terrorist activities. Thus, ammonium nitrate remains widely and readily available.
Accordingly, a need is identified for a cost efficient and effective method for providing an ammonium nitrate product which, while retaining agricultural benefits is significantly less prone to explosion, either accidental or through malevolent intent.